1. Field of the Invention
The present disclosure relates to light emitting diode (LED) units and, more particularly, to an LED unit comprising a lens having two aspheric surfaces.
2. Description of Related Art
LEDs, available since the early 1960's, have been increasingly used in a variety of applications, such as residential, traffic, commercial, and industrial settings, because of high light-emitting efficiency. A typical LED includes an LED die emitting light and a transparent encapsulant enveloping the LED die. The encapsulant protects the LED die from contamination and damage, and acts as a lens. However, due to size limitations of the encapsulant, the light cannot be significantly converged. The divergent light results in limited brightness of the LED. Therefore, light-adjusting devices, such as a catadioptric light distribution system, are utilized for further collimation of the light from the LED.
A typical catadioptric light distribution system includes a reflector mounted below and surrounding the LED, and a convex lens mounted above the LED. The reflector reflects light toward the lens from a perimeter of the encapsulant. The lens consolidates light emitted from the LED and reflected by the reflector into a single beam. Using the catadioptric light distribution system, most of the light emitted from the LED can be converged, and the brightness of the LED is increased.
However, since the lens of the catadioptric light distribution system is often spherical, the lens cannot effectively culminate the light into a narrow beam. The light incident on an opposite surface of the lens, after passing through the spherical surface of the lens, is still divergent, resulting in a scattered light beam, oriented away from the lens, and thus unsuitable for long-distance illumination.
What is needed, therefore, is an LED unit which can overcome the limitations described.